Method of forming an abrasive coating on a fan blade tip

ABSTRACT

A novel method of depositing grit particles onto a fan blade tip coating is provided. The method enhances grit capture by presenting a softened coating surface for the impinging particles. The softened surface is achieved without high substrate temperatures that could degrade the base metal properties in the fan blade. An auxiliary heat source is used to establish a locally heated and softened surface where the grit deposition takes place. The softened surface greatly increases the probability of grit capture.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/705,165 filed May 6, 2015, the disclosure of which is incorporatedherein by reference in its entirety.

FIELD OF THE DISCLOSURE

The subject matter of the present disclosure relates generally to amethod of finishing a rotating turbomachine component such as a fanblade. More particularly, the subject matter relates to a method offorming an abrasive coating on a fan blade tip of the type used in gasturbine engines.

BACKGROUND OF THE DISCLOSURE

Gas turbine engines, such as those used on jet aircraft, generallycomprise an air intake port, a fan section, a low pressure compressor(LPC) section, an intermediate section aft of the LPC section, a highpressure compressor (HPC) section, a combustion chamber or combustor,high and low pressure turbines that provide rotational power to thecompressor blades and fan respectively, and an exhaust outlet. The fanand LPC section may be operably connected to the low pressure turbine byan inner drive shaft which rotates about an engine center axis. Acone-like spinner may be mounted over the hub forward the fan blades tohelp guide air flow.

The fan section generally comprises fan blades mounted to a hub andenclosed within a fan case assembly. The fan case assembly generallycomprises a fan containment case and an abradable liner (a.k.a. outerair seal) disposed within the fan containment case. The clearancebetween the fan blade tips and the abradable liner is generally kept toa minimum for maximum engine efficiency.

One practice used in the aerospace industry to optimize the clearancebetween the fan blade tips and the abradable liner is to apply anabrasive coating on the fan blade tips, then operate the fan until theabrasive coating rubs off a desired amount of the abradable liner.

Examples of coatings for abradable liners can be found in U.S. Pat. Nos.3,575,427, 6,334,617, and 8,020,875. One exemplary baseline coatingcomprises a silicone matrix with glass micro-balloon filler. Without theglass micro-balloon filler, the elastic properties of the abradablecoating results in vibrational resonances and non-uniform rub response.The glass micro-balloons increase the effective modulus of the coatingso as to reduce deformation associated with aerodynamic forces andresonances. More recent proposals include fillers such as polymermicro-balloons (PCT/US2013/023570) and carbon nanotubes(PCT/US2013/023566).

For interfacing with the abradable liner, the fan blade tips may bear anabrasive coating. US Patent Application Publication 2013/0004328 A1,published Jan. 3, 2013, and entitled “Abrasive Airfoil Tip” discloses anumber of such coatings.

The present disclosure is directed to forming an abrasive coating on afan blade tip. Among other benefits, the method reduces heat generationwhen the fan blade tip rubs against the abradable liner.

SUMMARY OF THE DISCLOSURE

A novel method of forming an abrasive coating on a surface of a rotatingturbomachine component such as a fan blade tip is provided. The fanblade comprises an airfoil section and a tip. The airfoil section has ametallic substrate such as aluminum. The fan blade is mounted to a huband is configured to rotate within a fan case assembly. The fan caseassembly comprises an abradable liner made of an abradable material.

The method enhances grit capture by presenting a softened coatingsurface for the impinging grit particles. The softened surface isachieved without high substrate temperatures that could degrade the basemetal properties in the fan blade. An auxiliary heat source is used toestablish a locally heated and softened surface where the gritdeposition takes place. The softened surface greatly increases theprobability of grit capture.

In one aspect, the method comprises the steps of providing a feedstockof aluminum powder; heating the aluminum powder until the aluminumpowder is molten; spraying the molten aluminum powder onto a spray plumearea of the fan blade tip with a plasma spray gun to form a coating; anddepositing grit particles onto the coating while maintaining thetemperature of the coating within a desired range by controllingdeposition rate parameters.

The deposition rate parameters include aluminum powder feed rate,traverse rate of the plasma spray gun and the spray plume area.

The aluminum powder feed rate may be between about 20 g/min and 120g/min, and preferably between about 30 g/min and 60 g/min.

The traverse rate of the plasma spray gun may be between about 1200inches per minute and about 20 inches per minute, and preferably betweenabout 900 inches per minute and about 500 inches per minute.

The aluminum powder may be heated by introducing the powder into aplasma plume emanating from a plasma spray gun.

Before the depositing step the grit particles may be introduced into aplasma jet stream downstream from the plasma plume so the grit particlesdo not melt.

The grit particles should be harder than the abradable material in theabradable liner, which may be glass micro-balloons.

The airfoil section of the fan blade may comprise a metal-based materialsuch as aluminum or an aluminum alloy.

In another aspect of the disclosure the traverse rate of the plasmaspray gun may be varied during the spraying step.

In another aspect the plasma spray gun is directed along a spray path.The spray path may be varied to increase spray path spacing or toincrease or decrease spray overlap.

In another aspect the plasma spray gun has an axis of rotation and anaxis of powder injection substantially perpendicular to the axis ofrotation of the spray gun and, during the spraying step, the plasmaspray gun is rotated about its axis of rotation. The plasma spray gunmay be oriented with its axis of powder injection substantially parallelto the traverse direction (to minimize spray plume width) or in anyother orientation with respect to the traverse direction, and may changeduring spraying.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the concepts of the present disclosurerecited herein may be understood in detail, a more detailed descriptionis provided with reference to the embodiments illustrated in theaccompanying drawings. It is to be noted, however, that the accompanyingdrawings illustrate only certain embodiments and are therefore not to beconsidered limiting of the scope of the disclosure, for the concepts ofthe present disclosure may admit to other equally effective embodiments.Moreover, the drawings are not necessarily to scale, emphasis generallybeing placed upon illustrating the principles of certain embodiments.

Thus, for further understanding of these concepts and embodiments,reference may be made to the following detailed description, read inconnection with the drawings in which:

FIG. 1 is a partial side cross-sectional view of an exemplary gasturbine engine.

FIG. 2 is a perspective view of the fan section of a gas turbine engine,including a fan case assembly and fan blades.

FIG. 3 is a cross-sectional view of the fan section of FIG. 2 takenalong line 3-3 and showing a partial fan blade and a portion of theabradable liner 34.

FIG. 4 is a close up view of a fan blade tip and abrasive tip coatingaccording to the disclosure.

FIG. 5 is a schematic of a method of finishing a fan blade according tothe disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

In the disclosure that follows certain relative positional terms may beused such as “forward”, “aft”, “upper”, “lower”, “above”, “below”,“inner”, “outer” and the like. These terms are used with reference tothe normal operational attitude of a jet engine and should not beconsidered otherwise limiting. The forward end of a jet engine generallyrefers to the air intake port end and the aft end generally refers tothe exhaust end. Also, “radially outward” generally refers to adirection away from the engine center axis while “radially inward”refers to a direction toward the engine center axis. Finally, althoughthe following disclosure relates to a method of forming an abrasivecoating on a fan blade tip, it should be understood that the method maybe used with other components.

Turning to the figures, FIG. 1 is a longitudinal partial cross-sectionalview of an exemplary gas turbine engine 10. The gas turbine engine 10comprises an air inlet 12, a fan section 14, a single or multi-stagecompressor section 16, a combustion section 18 downstream of thecompressor section 16, a single or multi-stage turbine section 20, andan exhaust nozzle 22. Air entering the air inlet 12 flows through thecompressor section 16 and into the combustion section 18 where itprovides oxygen for fuel combustion. The hot combustion gases passthrough the turbine section 20 and exit the exhaust nozzle 22, providinga portion of the engine's thrust.

FIG. 2 is a perspective view of a fan section 14 as may be found in atypical gas turbine engine 10. The fan section 14 generally comprises aplurality of circumferentially-spaced fan blades 24 mounted to a hub 26and enclosed within a fan case assembly 28. The fan case assembly 28 maycomprise a thermally conforming liner 32 disposed within a fancontainment case 30. The fan containment case 30 is annular in shape andcircumscribes the fan blades 24.

The fan section 14 is designed such that the tolerance between the fanblades 24 and the fan containment case 30 is extremely small. To achievethis tolerance, the fan may be initially operated so that the fan blades24 rub against the fan containment case 30, as explained in more detailwith respect to FIG. 3.

FIG. 3 is a cross-sectional view of the fan case assembly 28 of FIG. 2,taken along line 3-3 and showing a partial fan blade 24 and a portion ofthe abradable liner 34. A portion of the thermally conforming liner 32disposed axially outward from the fan blades 24 is covered with anabradable liner 34 circumferentially mounted on a radially inner surface33 of the thermally conforming liner 32. The abradable liner 34 maycomprise an abradable rub material or coating and has an inboard surface36 in close proximity to the fan blade tips 25.

The abradable liner 34 may be formed of or coated with a polymeric basedmaterial, such as a polymer matrix composite. The polymeric basedmaterial may include an epoxy matrix and a silica-containing fillerdispersed through the matrix. In a further example, the abradablematerial may comprise a silica-containing filler that includes hollowglass micro-balloons, a.k.a. micro-bubbles or micro-spheres.

The fan blade 24 includes an airfoil section 38 that extends between aleading edge 40 and a trailing edge 42 and between a base 44 (FIG. 2)and a free tip 25. The fan blade tip 25 is covered with an abrasivecoating 46, the purpose of which is described below.

The airfoil section 38 of the fan blade 24 may be formed of ametal-based material and may have a polymeric overcoat on its exteriorsurface to protect the airfoil section 38 from damage due to foreignparticulates ingested into the engine 10. In one example, themetal-based material of the airfoil section 38 is aluminum or analuminum alloy. The polymeric coating can be a polyurethane-basedcoating, an epoxy-based coating, or a silicone rubber-based coating, butis not limited to these types of polymeric coatings or materials.

When two components, such as a fan blade tip 25 and an abradable liner34, are in rubbing contact, at least one of the components may wear. Theterm “abradable” refers to the component that wears, while the othercomponent is “abrasive” and does not wear or wears less. The word“abrasive” also implies that there is or can be contact with anabradable component. Thus, when the abrasive tips 25 of the fan blades24 rub against the abradable liner 34, the abradable liner 34 will beworn, whereas the abrasive tips 25 will not wear or will wear less thanthe abradable liner 34.

Friction between the fan blade tip 25 and the abradable liner 34generates heat. The heat can be conducted into the fan containment case30, into the fan blade 24, or both. However, in particular for metal fanblades 24 and polymeric-based fan containment cases 30, the metal of thefan blade 24 is generally a better thermal conductor than the polymer ofthe fan containment case 30, and a majority of the heat thus isconducted into the fan blade 24. While this may normally not present anyproblems for a plain metal fan blade 24, the heat conduction can bedetrimental to a metal fan blade 24 that has a polymeric overcoatbecause the heat can cause delamination of the polymeric overcoat andthus compromise the damage protection.

FIG. 4 is a close up view of a fan blade tip 25 according to thedisclosure. The fan blade tip 25 is covered with an abrasive coating 46comprising a metal matrix coating 48 and hard particles 50 deposited onor in the metal matrix coating 48. The metal matrix coating 48 and themetal-based material of the fan blade 24 may be compositionally composedof the same predominant metal, such as aluminum, which can promotestrong adhesion between the abrasive coating 46 and the fan blade 24.

FIG. 5 is a schematic of a method of finishing a fan blade 24 accordingto the disclosure. The method may comprise the following steps:

Providing a feedstock of aluminum powder.

Heating the aluminum powder until the aluminum powder is molten. Thealuminum powder may be introduced into a plasma plume emanating from aplasma spray gun (a.k.a. plasma spray torch), resulting in anelectrically heated gas jet stream. The heat energy from the plasmaspray gun is transferred to the aluminum powder particles, convertingthem into molten aluminum droplets. The molten droplets are thenpropelled toward the fan blade tip 25 by the gas jet stream.

Spraying the molten aluminum droplets onto an area of the fan blade tip25 to form an aluminum matrix coating 48. When the molten aluminumdroplets hit the surface of the fan blade tip 25 they spread out andcool rapidly due to conductive heat transfer, mainly into the metallicfan blade 24. At this point the droplets may be referred to as “splats.”Spraying can be done via a plasma spray gun.

Depositing grit particles 50 onto the aluminum matrix coating 48 via aplasma jet stream or other means, while maintaining the temperature ofthe aluminum matrix coating 48 by controlling certain deposition rateparameters as explained below.

The grit particles 50 may be introduced into the plasma jet streamdownstream from the plasma plume where the temperature of the plasma jetstream is lower. The grit particles 50 do not melt but remain angular inshape. Thus, if a sharp corner of a grit particle 50 hits the surface ofthe aluminum matrix coating 48 first, the sharp corner may create anindent into the still-soft aluminum matrix coating 48, and stick therevia mechanical embedding. Preferably the grit particles 50 are harderthan the abradable material in the abradable liner 34, which as notedabove can be glass micro-balloons.

The likelihood that any grit particle 50 sticks to the aluminum matrixcoating 48 is a function of certain “deposition rate parameters”. Thedeposition rate parameters may include the velocity of the grit particle50, the size and shape of the grit particle 50, the orientation withwhich the grit particle 50 impacts the aluminum matrix coating 48, thetemperature of the grit particles 50, and the “softness” and“stickiness” of the aluminum matrix coating 48, as well as the aluminumpowder feed rate, traverse rate of the plasma spray gun and spray plumearea.

Accordingly, during the deposition step, certain deposition rateparameters are controlled to optimize or otherwise control grit particledeposition. For example, the surface of the aluminum matrix coating 48can be intentionally made hotter to make it softer and stickier, i.e.,having a higher tendency to capture the grit particles 50.

Passive control of the deposition spot temperature can be achievedthrough control of the deposition rate parameters. For example, thedeposition spot temperature is generally directly proportional to thealuminum powder feed rate and the molten aluminum temperature, andinversely proportional to the spray plume area and traverse rate of theplasma spray gun.

Because aluminum is so heat conductive, there exists a high thermalgradient between the hot aluminum matrix coating 48 and the aluminum fanblade 24. As a consequence, heat is quickly conducted away from thealuminum matrix coating 48, which helps keep the temperature of thealuminum fan blade 24 in the vicinity of the aluminum matrix coating 48below an acceptable limit, thus protecting the mechanical properties ofthe fan blade 24. To counteract this phenomena, and to optimize thesurface temperature of the aluminum matrix coating 48 where the gritparticles 50 are being deposited, at least three deposition rateparameters may be controlled: aluminum powder feed rate, traverse rateof the plasma spray gun, and the area of the spray plume on the fanblade tip 25.

Aluminum powder feed rate. “Aluminum droplet flux” is the rate ofaluminum droplet deposition per given area of the fan blade tip 25, andmay be expressed in units of grams/minute/area, where the area isdetermined by the plume width times the distance traversed by the plasmaspray gun. Increasing the aluminum droplet flux by impinging more hotaluminum droplets on an area of the fan blade tip 25 over a given periodof time generally helps maintain the temperature of the aluminum matrixcoating 48 at an acceptably high level. But adding too much aluminumpowder to the plasma jet stream can result in poor heating (and melting)of the aluminum powder. The aluminum powder feed rate may be controlledto stay in an operable range of between about 20 g/min and 120 g/min.More preferably, the aluminum powder feed rate is between about 30 g/minand 60 g/min.

Traverse rate of the plasma spray gun. Traverse rate is the rate oflinear travel of the plasma spray gun across the surface of the fanblade tip 25, and may be expressed in units of distance/time. Increasingthe traverse rate by moving the plasma spray gun (or other thermal spraymeans) across the surface of the fan blade tip 25 more quickly resultsin a lower deposition of aluminum droplets per area, where area iscalculated as the traverse rate times the spray plume width. Thetraverse rate of the plasma spray gun may be between about 1200 inchesper minute and about 20 inches per minute. More preferably, the traverserate of the plasma spray gun is between about 900 inches per minute andabout 500 inches per minute. The plasma spray gun power may be 39kilowatts (kW) or higher. Too much power or a too slow traverse rate canmelt the aluminum substrate of the fan blade tip 25.

Spray plume area. As noted above, spray plume area is determined by thespray plume width and the distance traversed by the plasma spray gun.Heat flux is a measure of the rate of energy (heat) transfer through asurface per unit area. In this application heat flux is a measure of therate of heat transfer from the molten aluminum droplets through thesurface of the fan blade tip 25 for a given spray plume area. Increasingthe heat flux increases the temperature of the surface of the fan bladetip 25 which increases the grit deposition efficiency. Increasing thespray plume area on the fan blade tip 25 causes the heat flux todecrease, an undesirable effect. Therefore it is preferred that thespray plume is kept more concentrated (by decreasing the spray plumewidth as it traverses the fan blade tip 25) for the same number ofaluminum droplets, resulting in a higher heat flux.

Once the abrasive coating 46 is formed on the fan blade tip 25, the fanblades 24 are placed within a fan containment case 30 having anabradable liner 34. The fan is then operated so that the abrasive fanblade tips 25 wear out a portion of the abradable liner 34, creating anideal tolerance (spacing) between the fan blades 24 and the liner 34.

As noted above, the abradable liner 34 may comprise epoxy bonded glassmicro-balloons. If a smooth (“bare metal”) fan blade tip is rubbedagainst such an abradable liner 34, the temperature can increase to 700F or more due to frictional heating. Applying an abrasive to the fanblade tip 25 the harder grit particles 50 cut into the micro-balloons,resulting in high local pressures but lower, and better, temperatures.

Example

The method described herein has been shown to result in a depositionefficiency of about 45% (measured as the percentage of grit particles 50that stick to the metal matrix coating 48) compared to about 5.6% inbaseline methods. This increase in deposition efficiency results in anincrease in grit concentration in the abrasive coating 46, and higherwear resistance in service.

INDUSTRIAL APPLICABILITY

There has been described a novel method of depositing grit particles 50onto a metal matrix coating 48 that enhances grit capture by presentinga softened coating surface for the impinging grit particles 50. Thesoftened surface is achieved without causing the temperature of thesubstrate (i.e., the fan blade 24 in the vicinity of the metal matrixcoating 48) to exceed an acceptable temperature that could degrade thealuminum base metal properties in the fan blade 24. An auxiliary heatsource such as a laser or the heat of the spray process itself may beused to establish a locally heated and softened metal matrix coatingsurface where the grit deposition is taking place. The softened surfacegreatly increases the probability of grit capture.

The use of an auxiliary heat source for localized heating of the metalmatric coating 48 also provides localized temperature control (of themetal matrix coating 48) better than that which can be achieved usingpractical (conventional) spray parameters. The use of an auxiliary heatsource for localized heating of the metal matric coating 48 also allowsthe control of deposition rate parameters to levels chosen forconsiderations other than grit capture. The method may also be used tovary grit concentration locally by changing certain deposition rateparameters.

For example, local grit concentration can be locally controlled throughrelative torch to part motions. The simplest method to accomplish thiscontrol is to vary the traverse rate over the part to achieve a highersurface temperature and higher resultant grit concentration in an areawhere traverse is relatively slower. However, this method results inrelatively thicker coating in the area of reduced traverse speed. Thismay be overcome by locally reducing the number of time the torchtraverses over the area or by concurrently varying spray path spacingand related spray stripe overlap. Alternatively, rotational orientationof the spray torch about its axis may be used to adjust the width of thespray plume. This is achieved by taking advantage of the typicallyasymmetric powder and droplet distribution caused by substantiallyradial powder injection. By rotating the torch to position the powderinjection parallel to the traverse direction, the spray plume has itsminimum width, when it is perpendicular to the traverse direction, thespray plume is at its maximum width. Thus, by changing the rotationalorientation of the spray torch about its axis, particle flux may beadjusted to achieve the desired local control of abrasive gritconcentration in the coating.

What is claimed is:
 1. A method of forming an abrasive coating on arotating turbomachine component, the rotating turbomachine componentcomprising an airfoil section and a tip, the airfoil section and the tiphaving an aluminum or aluminum alloy substrate, the rotatingturbomachine component designed to rotate within an abradable liner madeof an abradable material, the method comprising the steps of: providinga feedstock consisting of aluminum powder; heating the aluminum powderuntil the aluminum powder is molten; spraying the molten aluminum powderonto the substrate of the tip with a plasma spray gun to form a coatingconsisting of aluminum, wherein the plasma spray gun has an axis ofrotation and an axis of powder injection, the plasma spray gun rotatableabout its axis of rotation; and depositing grit particles onto thecoating while maintaining a temperature of the coating within a desiredrange by controlling deposition rate parameters; wherein the depositionrate parameters include an aluminum powder feed rate of 20 g/min to 120g/min, a traverse rate of the plasma spray gun of 1200 inches per minuteto 20 inches per minute, the axis of powder injection oriented relativeto a traverse direction, and a spray plume area; wherein prior to orduring spraying, rotation of the plasma spray gun about its axis ofrotation changes the orientation of the axis of powder injectionrelative to the traverse direction.
 2. The method of claim 1, whereinthe orientation of the axis of powder injection relative to the traversedirection changes during spraying.
 3. The method of claim 1, wherein thealuminum powder feed rate is between about 30 g/min and 60 g/min.
 4. Themethod of claim 1, wherein the grit particles are harder than theabradable material in the abradable liner.
 5. The method of claim 1,wherein the traverse rate of the plasma spray gun is between about 900inches per minute and about 500 inches per minute.
 6. The method ofclaim 1, wherein the aluminum powder is heated by introducing the powderinto the plasma plume emanating from the plasma spray gun.
 7. The methodof claim 6, wherein before the depositing step the grit particles areintroduced into a plasma jet stream downstream from the plasma plume sothe grit particles do not melt.
 8. The method of claim 1, wherein therotating turbomachine component is a fan blade.
 9. The method of claim1, wherein during the spraying step the traverse rate of the plasmaspray gun is varied.
 10. The method of claim 1, wherein during thespraying step the plasma spray gun is directed along a spray path. 11.The method of claim 10, wherein the spray path is varied to increasespray path spacing.
 12. The method of claim 10, wherein the spray pathis varied to increase or decrease spray overlap.
 13. The method of claim1, wherein the plasma spray gun has an axis of rotation and wherein,during the spraying step, the plasma spray gun is rotated about its axisof rotation.
 14. The method of claim 1, wherein the plasma spray gun hasan axis of rotation and wherein, during the spraying step, the axis ofrotation changes.
 15. A method of forming an abrasive coating on a fanblade, the fan blade comprising an airfoil section and a tip, theairfoil section and tip having an aluminum or aluminum alloy substrate,the fan blade mounted to a hub and configured to rotate within a fancase assembly, the fan case assembly comprising an abradable liner madeof an abradable material, the method comprising the steps of: providinga feedstock consisting of aluminum powder; heating the aluminum powderuntil the aluminum powder is molten; spraying the molten aluminum powderonto the substrate of the fan blade tip with a plasma spray gun to forma matrix coating consisting of aluminum, wherein the plasma spray gunhas an axis of rotation and an axis of powder injection, the plasmaspray gun rotatable about its axis of rotation; and depositing gritparticles onto the matrix coating while maintaining a temperature of thematrix coating within a desired range by controlling deposition rateparameters; wherein the deposition rate parameters include an aluminumpowder feed rate of 20 g/min to 120 g/min, a traverse rate of the plasmaspray gun of 1200 inches per minute to 20 inches per minute, the axis ofpowder injection oriented relative to a traverse direction, and a sprayplume area; wherein prior to or during spraying, rotation of the plasmaspray gun about its axis of rotation changes the orientation of the axisof powder injection relative to the traverse direction.
 16. The methodof claim 15, wherein the grit particles are harder than the abradablematerial in the abradable liner.
 17. The method of claim 16, wherein theabradable liner comprises epoxy bonded glass micro-balloons.
 18. Themethod of claim 15, wherein the orientation of the axis of powderinjection relative to the traverse direction changes during spraying.19. The method of claim 15, wherein the plasma spray gun has an axis ofrotation and wherein, during the spraying step, the plasma spray gun isrotated about its axis of rotation.
 20. A method of forming an abrasivecoating on a rotating turbomachine component, the rotating turbomachinecomponent comprising an airfoil section and a tip, the airfoil sectionand the tip having an aluminum or aluminum alloy substrate, the rotatingturbomachine component designed to rotate within an abradable liner madeof an abradable material, the method comprising the steps of: providinga feedstock consisting of aluminum powder; heating the aluminum powderuntil the aluminum powder is molten; spraying the molten aluminum powderonto the substrate of the tip with a plasma spray gun to form a coatingconsisting of aluminum, wherein the plasma spray gun has an axis ofrotation and an axis of powder injection, the plasma spray gun rotatableabout its axis of rotation; and depositing grit particles onto thecoating while maintaining a temperature of the coating within a desiredrange by controlling deposition rate parameters; wherein the depositionrate parameters include an aluminum powder feed rate of 30 g/min to 60g/min, a traverse rate of the plasma spray gun of 900 inches per minuteto 500 inches per minute, the axis of powder injection oriented relativeto a traverse direction, and a spray plume area; wherein prior to orduring spraying, rotation of the plasma spray gun about its axis ofrotation changes the orientation of the axis of powder injectionrelative to the traverse direction.